The largest deal in the history of Swiss chocolate maker Lindt marks the culmination of over a decade's work for one Credit Suisse banker.

Lindt this week agreed to buy US-based confectionery group Russell Stover in what will be the biggest deal in its nearly 170-year history. Financial terms of the transaction were not disclosed but Dealogic estimates the price at around $1.4 billion.

The notoriously deal-shy Lindt has been a client of Jens Welter, global co-head of consumer and retail investment banking at Credit Suisse, for the last decade, according to a person familiar with the deal.

Welter joined the Swiss bank in 1995 and has advised the likes of consumer giants Coca-Cola, Heineken and Nestlé over the years. Lindt, however, has limited its activity to share buybacks in 2011 and 2013 while Welter has been on the account.

Still, Welter has met with the company at least once every two months during the last 10 years and speaks to management on a daily and weekly basis whenever they are considering strategic options, the person said.

Another investment banker working in the City of London described this week's deal as "pay day for 10-plus years of work”.

After joining Credit Suisse, Welter gained experience in the bank’s general M&A group, working on landmark transactions including Alcoa’s acquisition of Reynolds Metals Company in 1999.

His big break came after working on some of Nestlé’s biggest deals and he was promoted to run the consumer and retail investment banking team at 34 in 2007 – the same year he was named as one of Financial News's Rising Stars in investment banking.

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As one of Nestlé’s go-to advisers, he led its disposal of Alcon to Novartis in a two-step transaction valued at $39 billion in 2010, and this year advised the company on its deal to buy the rights to dermatology treatments from Valeant Pharmaceuticals, again valued at around $1.4 billion by Dealogic.

The Lindt deal is a particularly extreme example of what bankers often refer to as ‘long-term strategic advisory’. The company’s last takeover of size before this week's announcement came in 1998 when it bought US chocolate company Ghirardelli, based in San Francisco, for around $100 million. At the time, UBS advised the company.

By way of comparison, both Nestlé and Coca-Cola have completed north of 100 deals over that period, according to Dealogic.

A spokeswoman for Lindt said: “We really focus on chocolate and there are not so many opportunities in the market. We are a premium brand, we really don’t want to have too big a portfolio, we want to focus on making the best chocolate.”

Long-standing relationships with deal-shy companies have grown rarer as bankers have found it harder to make the economics of such arrangements work.

But the rewards can be two-fold. Lindt said in a statement that it is financing the acquisition in part through bank loans and, although it did not elaborate, Credit Suisse would be well placed to help out on the financing.

Marco Superina, a managing director in M&A based in Switzerland, also worked on the Lindt transaction for Credit Suisse. Goldman Sachs advised the seller, with US-based Andre Kelleners and Matt Gibson working on the deal.